An Australian Rivers Institute study has found that reef and mangrove habitats that are located close together have a greater abundance of fish and should be prioritised for conservation in marine reserves.
Andrew Olds, and colleagues from the Australian Rivers Institute (ARI) at Griffith University conducted the study in collaboration with the Queensland Department of Environment and Resource Management and the CSIRO.
They investigated whether connectivity between coral reefs and mangroves could improve the performance of marine reserves in the Moreton Bay Marine Park, Australia.
Their findings, reported in the journal Conservation Letters, show that connectivity between reefs and mangroves can enhance the ability of marine reserves to promote fish abundance.
In Moreton Bay, this translates to more harvested fish, particularly yellowfin bream, moses perch and black rabbitfish, in marine reserves where both reef and mangrove habitats occur in close proximity.
The research, which was funded by an ARC Linkage grant, found that in Moreton Bay, fish that migrate tidally between reefs and mangroves are influenced positively by reserve protection, habitat connectivity and diversity, and negatively by fishing and the length of tidal transition zones.
Conceptual diagram illustrating the importance of connectivity and habitat protection for yellowfin bream in Moreton Bay.
Connected habitats help maintain reef resilience
Marine reserves with well-connected reefs and mangroves also supported the greatest abundance of herbivorous fish. This suggests that connectivity may be important for maintaining ecological processes in reserves.
Herbivorous fish play a key role underpinning the resilience of coral reefs. They graze on fleshy algae, which compete with coral for living space, and their efforts can tip this competition in favor of coral.
Given the greater abundance of herbivores found in the connected habitats, reachers also expect increased grazing. This in turn should increase the resilience of protected reefs near mangroves.
With the major flooding of the Brisbane River into Moreton Bay over the 2010-2011 summer, this finding may have important consequences for the persistence and recovery of local coral reefs.
Incorporating habitat connectivity into conservation
Habitat connectivity can be incorporated into conservation strategies most simply using isolation distances, with ecologically appropriate thresholds being scaled to organism mobility.
The findings of the study concur with the isolation scale identified by recent papers from the Caribbean, suggesting that thresholds in mangrove-reef connectivity at scales of hundreds of metres may be widely applicable for conservation.
Olds and his colleagues, recommend that, where other factors are equal, connected habitats be considered higher priorities for conservation.
They warn that failure to incorporate connectivity into reserve assessment may undermine the value of conservation efforts.
Article reference:
Olds AD, Connolly RM, Pitt KA, Maxwell PS (2011) Habitat connectivity improves reserve performance. Conservation Letters. DOI: 10.1111/j.1755-263X.2011.00204.x
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